Objective Evaluate the diagnostic accuracy of the APPY1 Test alone and in combination with the Alvarado score (AS) to rule out acute appendicitis (AA) in patients presenting to EDs with abdominal pain suspicious for AA.

Methodology Observational study in a prospective consecutive cohort including all patients from 2 to 20 years with abdominal pain suggestive of AA in four EDs. The APPY1 Test was performed and AS was calculated to determine risk stratification for each patient.

Results 321 patients enrolled (mean age 11.8 (SD 3.8) years, 52.0% male), with 32.4% low risk, 23.7% intermediate risk and 43.9% high risk according to the AS. 111 (34.6%) had AA, of whom 1 (0.9%) had a false-negative APPY1 Test result. The APPY1 Test had a sensitivity (Se) of 99.1% (95% CI 94.4% to 99.9%), specificity (Sp) of 32.9% (95% CI 26.6% to 39.7%), negative predictive value (NPV) of 98.6% (95% CI 91.2% to 99.9%) and negative likelihood ratio (LHR−) of 0.03 (0.00 to 0.19) in this population. For patients at low risk by AS, the APPY1 Test had a Se of 100% (95% CI 62.9% to 100%), NPV of 100% (95% CI 91.1% to 100%) and LHR− of 0.0 (not calculable), and for patients at intermediate risk by AS, the APPY1 Test had a Se of 94.4% (95% CI 70.6% to 99.7%), NPV of 94.7% (95% CI 71.9% to 99.7%) and LHR− of 0.18 (0.0 to 1.2), respectively.

Conclusions APPY1 Test is a potentially useful diagnostic tool to rule out AA in this population, with clinical utility primarily in those patients classified as having low clinical risk of appendicitis according to the AS.